38 ASCIDIANS 



branch from the lower end of the phylum Chokdata, which 

 includes the Tunicata (or Urochordata), Balanoglossus and its 

 allies (Hemichordata), Amphioxus (Cephalochordata), and the 

 Vertehrata (or Craniata). Kowalevsky's great discovery has 

 since been confirmed and extended to all other groups of the 

 Tunicata by Kupffer/ Giard, and others. 



In 1872 Fol^ added largely to the knowledge of the 

 Appendiculariidae, and Giard ^ to that of the Compound 

 Ascidians. The latter author described a number of new forms 

 and remodelled the classification of the group. The most 

 important additions which have been made to the Compound 

 Ascidians since Giard's work have been the species described by 

 von Drasche,* from the Adriatic, and those discovered by the 

 " Challenger " expedition.^ The structure and the systematic 

 arrangement of the Simple Ascidians have been discussed of 

 recent years mainly by Alder ^ and Hancock, Heller,'' Lacaze- 

 Duthiers,* Traustedt,^ Eoule, Hartmeyer, Sluiter ^° and Herd- 

 man.^^ In 1874 Ussoff investigated the minute structure of 

 the nervous system and of the underlying gland, which was first 

 discovered by Hancock, and showed that the gland has a duct 

 which communicates with the front of the branchial sac or 

 pharynx by an aperture in the dorsal (or " olfactory ") tubercle. 

 In an important paper published in 1880, Julin ^^ drew atten- 

 tion to the similarity in structure and relations between this 

 gland and the " hypophysis cerebri " of the Vertebrate brain, and 

 insisted upon their homology. Metcalf has recently added 

 further to our knowledge on this and related matters. 



The Thaliacea or pelagic Tunicata have of late years been 

 the subject of several very important memoirs. The researches 



' Arch, ruikr. Anat. vi. 1872. 



- Mim. Soe. Fhys. Hist. Nat. Geneve, xxi. 1872. 



^ Arch. Zool. Exper. i. 1872. 



^ Synascidlen der Bucht von Hovigno, AVien, 1883. 



^ Challenger Reports, Tunicata, Part i. vol. vi. 1882 ; Part ii. vol. xiv. 1886 ; 

 Part iii. vol. xxvii. 1888. 



« Awn. Mag. Nat. Hist. (3) xi. 1863, p. 153 ; Journ. Linn. Soc. 1868, etc. 



' Denkschr. Akad. Wiss. Wien, 1875 and 1877. 



^ Arch. Zool. Expir. iii. 1874, and vi. 1877 ; Mhn. Instil. Paris, xlv. 1892. 



' Vid. Medd. Nat. For. Copenliagen, 1880, 1882, 1884, etc. 



" Nat. Tijdsehr. Ned.-Indie, 1885, etc. 



" Joiirn. Linn. Soe. Zool. xv. xxiii. and xxiv. ; Cat. of Tunicata in Australian 

 Mnseum, 1899 ; also Challenger Me^jorts (see note 6), 



^^ Arch, de Biol. ii. 



